Recently, organic light-emitting display devices have been attracting attention as plane type display devices of the next generation. They have excellent characteristics of natural light, wide view angles, fast response and so on.
Generally, an organic light-emitting element has a structure with a glass substrate which supports an organic light electroluminescent (EL) layer composed of a transparent electrode, e.g., of ITO, hole transporting layer, light-emitting layer, electron transporting layer and so on, and reflective electrode of low work function, where light emitted from the light-emitting layer is emitted from the back side of the substrate after passing through the electrode.
These organic light-emitting display devices can now have high efficiency and prolonged service life, when each of the organic layers is formed by vacuum deposition. R. Meerheim et al, for example, discloses that vacuum deposition can manufacture an organic red-color-emitting element having a brightness half period of 1,500,000 hours or more, when its initial brightness is 500 cd/m2 (Non-patent Document 1). The other methods for manufacturing organic light-emitting display devices include wet processes, e.g., spin coating and ink jetting for forming organic layers. An organic light-emitting display device manufactured by a wet process has a shorter service life and lower efficiency than an organic light-emitting element manufactured by vacuum deposition. Non-patent Document 2 discloses that an organic red-color-emitting element manufactured by spin coating using polymers has a service life of about 100,000 hours when its initial brightness is 500 cd/m2. The service life is about one-tenth that disclosed in Non-patent Document 1.
Recently, use of low-molecular-weight materials for forming films by embrocation has been studied. For example, Non-patent Document 3 discloses that an organic red-color-emitting element has a service life of at least 25,000 hours when its initial brightness is 500 cd/m2. The element has a shorter service life than the one manufactured by vacuum deposition using a low-molecular-weight material, disclosed in Patent Document 1. As discussed above, an element with a light-emitting layer manufactured by a wet process has a shorter service life than the one manufactured by vacuum deposition.
Organic light-emitting devices have been expected to find use for thin-film illuminators, thin-film display devices, illuminators for liquid-crystalline display devices. The light-emitting device is provided with a plurality of organic light-emitting elements forming pixels on a substrate. An organic light-emitting element has a structure with a plurality of organic layers disposed between upper and lower electrodes. The organic layers include hole transporting layer, electron transporting layer and light-emitting layer in which holes are recombined with electrons. When a voltage is applied between the electrodes, holes and electrons injected from the electrodes are recombined with each other in the light-emitting layer to emit light.
For example, Patent Document 2 discloses an organic light-emitting element having a stripe-shape lower electrode transmitting emitted light and upper electrode serving as a common electrode, wherein one of the electrodes is transparent. Power is supplied to each side of the lower electrode to diminish uneven brightness. The lower electrode, when transparent, has a high resistivity and suffers voltage loss around the center of the organic light-emitting device by wiring resistance, because of its high resistivity, to increase power consumption, even when power is supplied to each side. These troubles also occur with a transparent upper electrode.
Ink jetting is one of the processes for manufacturing organic layers for light-emitting display devices. For example, Patent Document 3 discloses a process comprising steps for forming a layer containing a first organic compound by embrocation, for heating the layer under a vacuum immediately before forming a layer, e.g., light-emitting layer, containing a second organic compound, and for forming the layer containing a second organic compound by vacuum deposition.